1. Field of the Invention
The present invention relates to a color selection mechanism for a color cathode-ray tube used in, for example, color television receivers, display apparatuses and so on.
2. Description of the Related Art
As a color selection mechanism for a color cathode-ray tube, an aperture grille (a color selection called an aperture grille) 30 as shown in FIG. 1 is known.
As for this color selection mechanism 30, there is provided a frame-shaped metal frame 32 which is formed of a pair of opposed support members 37U and 37D and elasticity applying or providing members 38R and 38L extended across the support member 37U to 37D. Between the opposed support members 37U and 37D of this frame 32, there is extended a so-called color selection electrode thin plate 31 having an arrangement including a large number of grid elements 33 and slit-shaped electron beam transmitting holes 35 formed between adjacent grid elements 33.
The support members 37 forming the frame 32 serve as beams for holding the thin plate. The elasticity providing members 38 have a property a spring, and serve as a bow for absorbing plastic deformation caused in the fabrication process of the cathode-ray tube and temporary extension caused by beam irradiation during the operation of the cathode-ray tube. The thin plate needs to have a predetermined tension so as not to cause shaking in the grid elements even for voices from a loudspeaker and an external vibration and shock.
When welding the thin plate to the frame 32, therefore, tension is applied to the thin plate in the extension direction xe2x80x9cgxe2x80x9d shown in FIG. 1, and compressive force (so-called turnbuckle) is applied to the support members 37U and 37D of the frame 32 conversely in such a direction xe2x80x9chxe2x80x9d as to pressurize and compress the space between the support members 37U and 37D.
After such welding is conducted, when the pressurization is removed, the compressive force of the frame 32 is released and the thin plate is fixed to the frame 32 in such a state that tension is always generated in the thin plate. If this tension is low, then the grid elements 33 are vibrated by an external shock, a vibration of the loudspeaker or the like, and consequently the impinging positions of the electron beam thereon are not fixed, resulting in color shifts and disturbed images.
Especially in such a frame that joint points of the support members 37 and the elasticity providing members 38 are selected at the ends of the support members 37, deflection at the central part of the support members 37 becomes large and hence a predetermined tension cannot be ensured, resulting in a problem.
As shown in FIG. 2A, the frame 32 of the color selection mechanism 30 has an L-shaped section. The frame 32 has such a shape that a longitudinal length xe2x80x9chxe2x80x9d and a lateral length xe2x80x9cdxe2x80x9d of the L shape are the same in both its central part and end parts. The position and thickness of the frame 32 are determined so as to minimize an interference margin distance xe2x80x9cmxe2x80x9d between an end part 37d of the support 37 and an electron beam E.
For pressurizing the frame 32 and obtaining a predetermined tension distribution over the whole surface of the thin plate, the support members 37 must be tough, and increased weight of the frame 32 poses a problem. Therefore, attempts to increase the mechanical strength (geometrical moment of inertia) has been made. For example, the plate thickness of the support members 37 is increased while maintaining margin distance xe2x80x9cmcxe2x80x9d and xe2x80x9cmexe2x80x9d for the electron beam E. Furthermore, the dimension of the L shape as a whole is increased by suitably selecting the horizontal/lateral ratio h/d of the dimension of the L shape as shown in FIG. 2B (although the horizontal/lateral ratio h/d is constant in the range from the end parts to the central part), or the like.
Since the conventional support members 37 are shaped so that the end parts and the central part will have the same sectional shape (i.e., the same longitudinal/lateral ratio of the dimension of the L shape), however, the mechanical strength is determined on only the plate thickness from the problem of the electron beam cut, and consequently the degree of freedom of the design is low.
Especially, in a frame for a large sized tube, the weight becomes extremely large. The increased frame weight not only increases the cost but also aggravates the shock resistance of the cathode-ray tube. In addition, it is necessary to prepare various kinds of plate thickness of the frame material according to predetermined strength values of model units, and hence it is difficult to decrease the stock of materials.
Furthermore, in the above described improvement method, fabrication is difficult and the cost increases significantly. For its application to a general purpose cathode-ray tube; therefore, there are many problems.
In view of the above described points, an object of the present invention is to provide a cathode-ray tube and its color selection mechanism having an excellent quality and improved in mechanical strength without being increased in weight by improving the shape of the support members.
According to a color selection mechanism of the cathode-ray tube of the present invention, a geometrical moment of inertia representing the mechanical strength of a frame can be freely set by changing a ratio of a longitudinal dimension to a lateral dimension of an L-shaped section of each support member stepwise from a central part of each support member to each of end parts thereof without changing the whole width of the L-shaped section.
According to the color selection mechanism of the present invention, it becomes possible to increase the mechanical strength of the frame by using a single material without increasing the weight of the support member. In particular, it becomes possible to improve the shock resistance of a large-sized cathode-ray tube. And it becomes possible to reduce the manufacturing cost thereof.
According to a cathode-ray tube of the present invention, there is provided a color selection mechanism in which a ratio of a longitudinal dimension to a lateral dimension of an L-shaped section of each of a pair of support members is changed stepwise from a central part of each of the pair of support members to end parts thereof. As a result, it becomes possible to increase the mechanical strength of the central part of the support members without increasing the weight of the frame itself. Since the tension of the central part of the color selection electrode thin plate can be increased, the shock resistance of the cathode-ray tube can be prevented from being aggravated by an increase of the frame weight.